~ an enthusiastic meddler exploring photography

Extension Tubes

One of the problems when trying to take extreme close-up photographs is that most lenses have a limit on how close the subject can be and still be able to focus on it. Since lenses focus closer by moving one or more elements further from the film/sensor plane this is usually a design compromise; to keep the lens compact the range of focus is limited. Dedicated macro lenses like my Canon FD 50mm 1:3.5 Macro S.S.C. often have a much longer focus range making them a lot longer than standard lenses with the same focal length. Even then there has to be a limit to the length of the lens, so if you want to get even closer to your subject what do you do?
One option is to use extension tubes. An extension tube is more or less what it sounds like – it’s a rigid tube that sits between the camera and the lens. Because the lens is now further away from the sensor plane it can focus on subjects much more closely. Unlike a teleconverter (or “Extender” as Canon calls them) which also fits between camera and lens an extension tube has no optical elements built in and so has no effect on the image quality other than to require slightly increased exposure times because of the increased distance of lens to sensor. As it’s just an empty tube you can use them with pretty much any lens in your collection too.

At the most basic level an extension tube can be made by taking a camera body cap and a rear lens cap, cutting a large hole in each one, and joining them securely on each end of a length of plastic pipe. How much trust you put in such a construction to securely mount a lens to a camera probably depends upon the price of replacing that lens. A better option is to get some proper extension tubes, especially if you want to use modern lenses with autofocus and no manual aperture. A decent compatible set of tubes will allow full camera control of the lens as if it was attached normally. With Canon at least this just requires the correct electrical connections to be made – other systems may vary – so there’s no need to necessarily buy Canon’s own tubes which command a high premium. Since there’s no optical element it’s hard to justify the full price of some of these tubes.

For some rarer cameras you may have little choice but to look for an official set, exactly the situation I found myself in with my Bronica. The S2A is an old camera and while not rare exactly, it is obviously a limited market and third party accessories are uncommon. I posted before about the bellows attachment I purchased, which is essentially a continuously variable extension tube, and while this lets me do some pretty amazing close up work, it’s essentially a studio tool, and much too awkward to work with out and about. So I hunted around on e-bay and found a set of Bronica extension tubes, in good condition, complete with box – as pictured.

The Bronica set consists of four parts C-A, C-B, C-C, C-D, which can be combined in various ways to give different extensions. The minimum option is to use the C-A tube on its own as this provides control over the lens aperture. One slightly unusual feature of the Bronica tube set is that only the C-A tube uses the normal lens bayonet-type mount, the other three tubes use the additional screw mounting inside the bayonet. My guess it that with the medium format lenses tending to be relatively large and heavy this avoids stress on the bayonet fitting and provides a more secure mount.

The tubes are much more portable than the bellows, but they can also be used with the bellows for even more extension. The magnification possible varies according to the focal length of the lens used but with this test shot I used all four tubes and the bellows together with the standard Nikkor-P 75mm 1:2.8 lens.

The magnification here is at least 2:1 at the film plane – that is the image on the film is twice the size of the real object. Using a shorter focal length the magnification can get much higher but at the expense of the object being so close to the lens that it’s very hard to light it properly. Other challenges with the full bellows and tubes set-up are that the viewfinder gets very dark, and focus is awkward – usually the easiest way to focus is to move the subject, rather than adjust the camera.

However, just using one or two of the extension tubes is much simpler, and can be useful with the longer lenses. For example my Nikkor-P 200mm 1:4 normally has a minimum focusing distance of 3.3 metres which is limiting for portrait situations as it’s not close enough for a head and shoulders view. Adding just the C-A seems to give a much nicer frame for portraits as seen in this last photograph, although admittedly the angel is a little smaller than “life” size.